JPH05138162A - Production of ultra pure water - Google Patents

Abstract

PURPOSE:To produce ultra pure water with an extremely little content of the total organic carbon. CONSTITUTION:After pure water with <=10ppm total organic carbon is irradiated by ultraviolet rays with short wavelength, it is passed through a mixed bed of cation exchange resin and anion exchange resin at >=100SV. Therefore, the influence of eluted substances from ion exchange resin is kept to a minimum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing ultrapure water. In particular, the present invention relates to the production of ultrapure water having a very low total organic carbon content required for the production of VLSI.

[0002]

2. Description of the Related Art Ultrapure water is produced by further refining the pure water obtained by a pure water producing apparatus. Various types of pure water production devices have been developed and put into practical use according to the characteristics required for pure water. Above all, the ultrapure water used in the manufacture of VLSI has extremely strict requirements, so
The deionized water producing device is also a highly sophisticated device that combines an ultraviolet irradiation means, an ion exchange means, a membrane separation means and the like.
Fig. 1 is one of the representative ones. Raw water is subjected to pretreatment consisting of coagulation filtration and two-bed, three-column type ion exchange.
Ultraviolet irradiation means, a vacuum degassing tower and a primary deionizer comprising a mixed bed of a strongly acidic cation exchange resin and a strongly basic anion exchange resin, and a secondary deionizer comprising a reverse osmosis membrane,
It is taken out as pure water. The water quality of this pure water is, for example, a specific resistance of 18 MΩ · cm or more and a total organic carbon content of 20 ppb.
Has reached the following: This pure water is further purified to obtain ultrapure water. This process is commonly referred to as the subsystem,
In a typical example thereof, as shown in FIG. 1, pure water is irradiated with short-wavelength ultraviolet rays to decompose contained organic matters into carbonic acid or organic acid, and then anion polisher which is a strongly basic anion exchange resin bed. Then, the mixture is passed through a cartridge polisher, which is a mixed bed of a strongly acidic cation exchange resin and a strongly basic anion exchange resin, to remove ionic substances, and then ultrafiltration is performed to remove colloidal fine particles and the like. Use ultrapure water. The quality of the ultrapure water thus obtained has a specific resistance of 18 MΩ · cm or more, a number of fine particles of 0.07 μm or more of 5 or less, a viable cell number of 10 or less, and a total organic carbon content of 1 to 1. It has reached 5 ppb.

[0003]

With the recent improvement in the degree of integration of VLSIs, the total organic carbon content of ultrapure water is 1p.
Those below pb have been required. However, it is difficult to constantly produce ultrapure water having a total organic carbon content of 1 ppb or less, even if pure water is repeatedly irradiated with the short-wavelength ultraviolet light and treated with an ion exchange resin.

Therefore, the present invention has a total organic carbon content of 1 p.
It is intended to provide a method for constantly and easily producing ultrapure water of pb or less.

[0005]

According to the present invention, the velocity of pure water passing through the cartridge polisher, which is the final stage of the ion exchange resin treatment in the production of ultrapure water, is 1 in space velocity.
By using a high speed of 00 or more, preferably 200 or more, contamination by the eluate from the ion exchange resin can be minimized, and ultrapure water with an extremely low total organic carbon content can be produced. ..

According to the knowledge of the present inventors, in the production of ultrapure water, the eluate from the ion exchange resin has a great influence on the total organic carbon content of the obtained ultrapure water. It is well known that, in various treatments using an ion exchange resin, the eluate from the ion exchange resin may be contained in the treatment liquid. The eluate from the ion exchange resin can be reduced by washing the ion exchange resin, and various washing methods have been developed according to the use of the ion exchange resin. In the process of purifying pure water into ultrapure water, ion exchange resins with extremely reduced eluates are used. However, it is impossible at present to completely remove the elution from the ion exchange resin.

As a result of detailed examination of the elution of organic substances from the ion exchange resin, the present inventors have found that the elution rate is controlled by the diffusion of the eluate within the resin particles. For example, in FIG. 2, pure water obtained in the ultrapure water production process of FIG. 1 is irradiated with short-wavelength ultraviolet light, and then a mixture bed of a strongly acidic cation exchange resin and a strongly basic anion exchange resin (mixing ratio is exchanged). Volume ratio 1: 1 and volume ratio 1: 1.
7 is a graph showing the relationship between the space velocity and the total organic carbon content of ultrapure water at the outlet of the mixed bed when 7) is passed at various flow rates. (Note that in the present invention, the space velocity is calculated by taking the volume of the mixed bed as the sum of the volume of the cation exchange resin and the volume of the anion exchange resin.) FIG. It is the graph displayed on the relationship between the quantity and the reciprocal of space velocity.

The total organic carbon content was measured using A-100 PSE manufactured by Anatelle. This A
The measuring principle of -100PSE is to irradiate water with short-wavelength ultraviolet light to decompose organic substances, obtain the amount of carbonic acid generated by this from the change in resistivity of water, and obtain the total organic carbon content from this amount of carbonic acid. Is. As is clear from FIG. 3, in the region where the space velocity is large, the graph shows a linear relationship between the total organic carbon content of the ultrapure water and the reciprocal of the space velocity, and the elution rate of the organic substances from the ion exchange resin is the resin. It is shown that it is diffusion controlled within the grain. The fact that the total organic carbon content of the ultrapure water is below the straight line in the region where the space velocity is small indicates that the influence of the film diffusion on the surface of the resin particles is shown.

In the present invention, pure water is supplied at a space velocity of 100.
Thus, the ion exchange resin bed is passed. It is usually passed through the ion exchange resin bed at a flow rate of 120 or more, especially 200 or more. The higher the space velocity, the more the influence of the eluate from the ion exchange resin can be avoided, but the pressure loss when passing through the ion exchange resin bed increases, and the impurities to be trapped in the ion exchange resin bed are trapped. Instead, the risk of leakage into ultrapure water increases. Furthermore, in ultra-LSI manufacturing plants, ultra-pure water production equipment is required for at least 120 days (4 months),
Normally, continuous operation is performed for 180 days (6 months), so if the space velocity is too high, the exchange capacity of the resin bed will be insufficient, the quality of ultrapure water will deteriorate, and there is a risk that the continuous operation time will be shortened. is there. Therefore, the space velocity is 500 or less, especially 400
It is preferable to stop below.

In the present invention, ultrapure water is produced by a conventional method except that the space velocity when passing through the final ion-exchange resin bed in the process of purifying pure water into ultrapure water is 100 or more. be able to. For example, the pure water production, which is the pre-stage of the ultrapure water production, may be carried out using a conventional apparatus comprising a pretreatment apparatus-a primary pure water apparatus-a secondary pure water apparatus. The quality of pure water is preferably 18 MΩ · cm or more in specific resistance and 20 ppb or less in total organic carbon content. In the process of purifying the pure water of the present invention into ultrapure water, the space velocity when passing through the ion exchange resin bed is remarkably high. May not reach the desired value, or the water quality of the ultrapure water may deteriorate before the desired continuous water passage time is reached. Organic matter in pure water is decomposed into carbonic acid or carboxylic acid by irradiation with short-wavelength ultraviolet light and captured by the ion exchange resin. Therefore, if this amount is large, the load on the ion exchange resin increases, and the ultrapure water is the same as described above. There is a risk that the water quality will deteriorate and the treatment time for continuous water flow will be shortened. Therefore, the organic matter in pure water is preferably 10 ppb or less, and particularly preferably 5 ppb or less.

In the process of purifying pure water into ultrapure water, the organic substances in the pure water are first decomposed by irradiation with ultraviolet rays, and then anion polisher and cation exchange resin which are anion exchange resin beds are used, as in the conventional method. It is advantageous to use a method in which a cartridge polisher, which is a mixed bed of cation and anion exchange resin, is passed in this order, and finally ultrafiltration is performed to obtain ultrapure water. The anion polisher may be omitted in some cases, but it is desirable to use them in order to stably produce ultrapure water having a constant water quality.

It is necessary for the ultraviolet rays to be short-wavelength ultraviolet rays having a large decomposing power for organic substances, and those having a wavelength of 185 nm are usually used. The amount of UV irradiation may be determined by the amount of pure water organic matter, but normally the amount of water flow is 1 m ³
The amount of ultraviolet rays is 0.1 to 0.5 KW · h per hour. Pure water that has been irradiated with ultraviolet rays captures carbonic acid and carboxylic acid produced by the anion polisher. The space velocity with respect to the anion polisher is also preferably 100 or more, and particularly preferably 200 or more. If the organic matter in the pure water is 10 ppb or less, preferably 5 ppb or less, no leakage of impurities occurs for at least 4 months, usually 6 months even if water is passed at a space velocity of 200, and even if it leaks. It can be completely captured by the next cartridge polisher. Cartridge polisher is the last ion exchange resin treatment in ultrapure water production, and as described above, the space velocity is 100 or more, preferably 20.
Pass water at 0 or more to avoid contamination by eluate as much as possible. The composition of the cartridge polisher may be appropriately determined depending on the water quality at the inlet, but usually the exchange capacity ratio of the cation exchange resin and the anion exchange resin is 1 :.
2 to 2: 1.

The treated water that has passed through the cartridge polisher is then subjected to ultrafiltration to remove colloidal substances and the like contained in an extremely small amount, and then used as ultrapure water for various purposes. In the present invention, the amount of eluate from the ion exchange resin is extremely low, so that clogging of the ultrafiltration membrane hardly occurs.

[0014]

According to the present invention, the influence of the eluate from the ion exchange resin can be suppressed to a minimum, so that ultrapure water having a total organic carbon content of 1 ppb or less can be stably produced. it can.

[Brief description of drawings]

FIG. 1 is a flow sheet of an example of an ultrapure water production system.

FIG. 2 shows the space velocity and the total amount of ultrapure water at the outlet of the mixed bed when pure water irradiated with short-wavelength ultraviolet light is passed through the mixed bed of the strongly acidic cation exchange resin and the strongly basic anion exchange resin. It is a graph which shows the relationship with an organic carbon content.

FIG. 3 is a graph showing the graph of FIG. 2 as a relationship between the reciprocal of space velocity and the total organic carbon content.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C02F 9/00 Z 6647-4D

Claims (10)

[Claims] 1. Pure water having a total organic carbon content of 10 ppb or less is irradiated with short wavelength ultraviolet rays, and then the pure water is passed through a mixed bed of a cation exchange resin and an anion exchange resin at a space velocity of 100 or more. And a method for producing ultrapure water. 2. The method for producing ultrapure water according to claim 1, wherein the total organic carbon content of the pure water irradiated with short-wavelength ultraviolet light is 5 ppb or less. 3. The method for producing ultrapure water according to claim 1, wherein pure water irradiated with short wavelength ultraviolet rays is passed through the mixed bed at a space velocity of 200 or more. 4. The production of ultrapure water according to any one of claims 1 to 3, wherein pure water irradiated with short-wavelength ultraviolet light is passed through an anion exchange resin bed and then through a mixed bed. Law. 5. The method for producing ultrapure water according to claim 4, wherein pure water irradiated with short wavelength ultraviolet rays is passed through the anion exchange resin bed at a space velocity of 100 or more. 6. The method for producing ultrapure water according to claim 1, wherein pure water irradiated with short-wavelength ultraviolet rays is continuously passed through the mixed bed for at least 120 days. 7. The method for producing ultrapure water according to any one of claims 1 to 6, wherein pure water irradiated with short-wavelength ultraviolet light is passed through a mixed bed and then passed through an ultrafiltration membrane. .. 8. Pure water obtained from a pure water production process including an ultraviolet irradiation means, an ion exchange means, and a membrane separation means is irradiated with short-wavelength ultraviolet light, and then applied to a mixed bed of cation exchange resin and anion exchange resin. A method for producing ultrapure water, characterized in that the ultrapure water is passed at a space velocity of 100 or more. 9. The method for producing ultrapure water according to claim 8, wherein pure water irradiated with short-wave ultraviolet rays is passed through an anion exchange resin bed and then passed through a mixed bed. 10. The method for producing ultrapure water according to claim 9, wherein pure water irradiated with short-wavelength ultraviolet rays is passed through the anion exchange resin bed at a space velocity of 100 or more.